Abiogenesis

Abiogenesis Definition

Abiogenesis is the creation of organic molecules by forces other than living organisms. While organisms can create carbon-carbon bonds relatively easily thanks to enzymes, to do so otherwise requires large inputs of energy. Early in the history of science, this fact was used to dispute evolution, as it could not be conceived how organic molecules could be produced from non-organic sources. The theory of abiogenesis as an evolutionary theory was given much credit when Stanley Miller conducted his famous experiment trying to prove the inorganic beginning of life.

Miller combined various gases that were though to exist in the earliest stages of Earth. These gases were combined in a chamber, and shocked with large amount of electricity for weeks at a time. After the trial, Miller would analyze the samples. He found that the molecules had begun the process of combining into more advanced molecules. Miller theorized that over billions of years, these molecules could combine into self-replicating versions, such as RNA and DNA. Further laboratory experiments confirmed these findings in later decades. Several very precise experiments have provided sufficient evidence that many of the molecular structures of cells could be created from inorganic solutions with an input of energy. Polypeptides (proteins) and RNA have both been synthesized in this way.

The synthesis of both proteins and RNA in the laboratory is a crucial piece of evidence for abiogenesis theory. It is though that the abiogenesis of these molecules could lead to self-replicating RNA molecules. Both proteins and RNA molecules are known to act as catalysts. These molecules, produced by abiogenesis, could catalyze important reactions that could lead to the replication of RNA and the production of complexes such as ribosome, which translate proteins from RNA messages. The formation of these two molecules through abiogenesis proves that the first steps in abiogenesis theory could have taken place. Due to the large amount of energy used, some scientists argue that abiogenesis theory does not consider the amount of lightning and other energy sources in the early atmosphere.

Abiogenesis Theory

Abiogenesis theory is the theory that all life started from inorganic molecules, which recombined in different ways due to energy input. These different forms eventually formed a self-replicating molecule, which may have used the other molecules produced by abiogenesis to start creating the basic structures of life, such as the cell.

Just as populations change over time in the evolution of organisms, the evolution of molecules involves the changing of molecules over time. Scientist speculate that the first self-replicating molecules were probably RNA molecules. Some RNA molecules have a known ability to catalyze the formation of new RNA molecules, as seen in the ribosomes of nearly all creatures on Earth. One of these early RNA molecules formed just right, so that it produced an RNA molecule that was identical to it. The concentration of this molecule in the prebiotic soup increased drastically, and the molecule further interacted with itself and some proteins formed around it, also through abiogenesis.

Eventually, the RNA molecule acquired mutations that allowed it to synthesize a protein that would produce more RNA. Other mutations caused proteins to be created that synthesized strands of DNA from RNA. Thus, the genome of the modern organism was born. Over millions of years of evolutionary history, changes slowly accumulated in these molecules, giving rise to the complexity of life we see today. Various scientist that study abiogenesis theory argue over the exact point that abiogenesis switches to biogenesis. Similar arguments can be seen in the case of whether or not viruses constitute living organisms. Abiogenesis, by definition, is simply the creation of organic molecules from inorganic sources. It does not necessarily imply where life begins.

Related Biology Term

Evolution – The process that changes populations of organisms over time, adapting them to the environment.

Inorganic – Molecules containing little carbon, not made in living organisms.

Organic – Molecules synthesized in living organisms that contain many carbon-carbon bonds.

Ribosome – One of the first cellular machines, capable of producing proteins from RNA molecules and amino acids.

Quiz

1. A virus attached to a cell, and injects it DNA into a cell. The cell’s proteins and structures create proteins from the DNA, which create more viral DNA and protein cases. Currently, viruses are not considered to be “living”. Is this abiogenesis?A. Yes, because the virus is not a living organisms but it is creating proteins.B. No, because the cell is still responsible for the new materials.C. Yes, but only if there is no carbon in the new material.

Answer to Question #1

B is correct. Part of the reason that viruses are not considered living organisms is that they do not synthesize their own new materials. However, living cells do synthesize the new materials. Therefore, this is not a case of abiogenesis. The presence of carbon only makes the molecule inorganic or organic depending on where the molecules were synthesized.

2. Which of the following is a valid criticism of abiogenesis theory?A. The levels of energy needed to produce self-replicating molecules isn’t possible outside the lab.B. We cannot known what the atmosphere of pre-Earth looked like.C. If RNA formed first, there would be no reason for DNA.

Answer to Question #2

B is correct. This is often used as a defense against abiogenesis theory. While there are several methods that can study rock formations and the chemical compositions they contain to predict what the atmosphere was like, it is impossible to known for sure. Further, it is usually assumed that there was enough time and energy from lightning input to create these molecules. Between the time the Earth formed and the oldest living organisms have been dated, there is well over a billion years. Although RNA probably formed first, DNA is a much more stable molecule, and there are many advantages for organisms to use DNA to store their genetic code.

3. Why would molecules naturally combine in nature?A. They are naturally attracted to each other.B. The products of their reactions are more stable.C. All of the above.

Answer to Question #3

C is correct. Some molecules simply have a tendency to combine. Oxygen, for example, tends to exist bonded to other oxygen molecules, in pairs. Sodium and chlorine atoms tend to be attracted to each other and form a matrix of atom in nature called salt. Larger molecules are subject to the same forces. One of the key points in abiogenesis theory is that some molecules will naturally aggregate and form, simply due to physics.